I remember driving in Wisconsin quite a long time ago and noticing that they used that steel that rusts for five years creates a coating and then never needs painting again. It is extremely expensive, but long term is self sustaining and impervious to deterioration for all intents and purposes. I noticed how smooth the roads were also and asked someone and they said that the state had put a whole lot more into the original roads including and especially the base so that the long term maintenance costs would be sharply reduced.
I haven't been in Wisconsin for like 25 years, so can't attest to much more than what I noted above. I have seen some bridges made out of that steel since, but they usually are bridges where the maintenance would be difficult like way up in the air. Growing up in Indiana, the roads used to be good, but since it has grown so much, I too have noticed all the work around the edges, like what is this carve out a two foot by four foot section along the edge every 200 feet and put asphalt in it that six months later is cupped and a bear to drive over. I'm thinking its that base showing wear at the seams of the slabs.